1. Field of the Invention
The present invention generally relates to multi-piece golf balls and more particularly to golf balls having at least one layer made of polyamide/acid anhydride-modified polyolefin compositions. The golf ball includes a core having at least one layer and a cover having at least one layer. Preferably, the ball contains a dual-core having an inner core and surrounding outer core layer or a multi-layered core having an inner core, intermediate core layer, and outer core layer. Preferably, at least one of the core layers is formed from a composition comprising a blend of polyamide and acid anhydride-modified polyolefin and fatty acid salt and/or amide.
2. Brief Review of the Related Art
Multi-piece, solid golf balls are used today by recreational and professional golfers. Basically, these golf balls contain an inner core protected by a cover. The core acts as the primary engine for the ball and the cover helps provide the ball with durability and wear-resistance. The core and cover may be single or multi-layered. For example, three-piece golf balls having an inner core, inner cover layer, and outer cover layer are popular. In other instances, golfers will use a four-piece ball containing a dual-core (inner core and surrounding outer-core layer) and dual-cover (inner cover layer and surrounding outer cover layer). Intermediate (casing) layer(s) may be disposed between the core and cover layers to impart various properties. Thus, five-piece and even six-piece balls can be made. Normally, the core layers are made of a natural or synthetic rubber material or highly neutralized ionomer polymers (HNPs). These ionomer polymers are typically copolymers of ethylene and methacrylic acid or acrylic acid that are partially or fully neutralized. Metal ions such as sodium, lithium, zinc, and magnesium are used to neutralize the acid groups in the copolymer.
Such ethylene acid copolymer ionomer resins are relatively hard materials having good durability, cut-resistance, and toughness. The ionomers may be used to make cover, intermediate, and core layers. When used as a core material, the hard ionomer resin helps impart a higher initial velocity to the golf ball. This is particularly advantageous for driver shots off the tee. The ball tends to have good flight distance. However, one disadvantageous feature of such balls is they tend to have a hard “feel.” Some players experience a harsher, less comfortable feel when their club face makes contact with these hard balls. The player senses less control and the harder ball tends to have low initial spin. It is generally more difficult to hit hard balls with the proper touch and control. This can be particularly troublesome when making approach shots with irons near the green.
Thus, the industry has looked at numerous non-ionomeric materials such as polyolefins, polyamides, polyesters, polyurethanes, polyureas, fluoropolymers, polyvinyl chlorides, polycarbonates, polyethers, polyimides, and the like for making components and layers in golf balls. For example, Kim et al, US Patent Application Publication US 2010/0167845 discloses golf balls having a core, at least one intermediate layer, and at least one cover layer prepared from blends of polyamides with functional polymer modifiers of the polyamide. The functional modifier of the polyamide can include ∞-olefin copolymers or terpolymers having a glycidyl group, hydroxyl group, maleic anhydride group, or carboxylic group. The polyamide composition is preferably blended with a polyalkenamer rubber/functionalized organic modifier material.
Sullivan et al., U.S. Pat. No. 6,872,774 discloses a multi-layered golf ball having a core, intermediate layer, and cover. The intermediate layer is made of a composition comprising a non-ionomeric acid polymer and non-ionomeric stiffening polymer including blends of polyamides and polypropylene and polyethylene copolymers that have been grafted with maleic anhydride or sulfonate groups.
In Rajagopalan et al., U.S. Pat. No. 6,800,690 golf balls having at least one layer formed from a composition comprising a polyamide and non-ionomeric material including grafted or non-grafted metallocene-catalyzed olefinic polymers such as polyethylene and copolymers of ethylene are disclosed. The olefinic polymers may also contain functional groups such as epoxy, anhydride, amine, oxazoline, sulfonic acid, carboxylic acid, and their salts.
Although some non-ionomeric compositions containing polyamides as mentioned above may be somewhat effective for making certain components and layers in a golf ball, there is still a need for new compositions that can impart high quality performance properties to the ball. Particularly, there is a continuing need for improved core constructions in golf balls. The core material should have good toughness and provide the ball with high resiliency. The core material, however, should not be excessively hard and stiff so that properties such as feel, softness, and spin control are sacrificed. The present invention provides golf balls having an optimum combination of properties.